[....]
  LD      init/built-in.o
  LD      .tmp_vmlinux1
kernel/built-in.o(.kprobes.text+0xa3): In function `get_insn_slot':
: undefined reference to `module_alloc'
kernel/built-in.o(.kprobes.text+0x1f3): In function `free_insn_slot':
: undefined reference to `module_free'
----------------------------------------

module_alloc() and module_free() functions are only compiled in when 
CONFIG_MODULES are enabled. So if CONFIG_MODULES are disabled we get the above 
compile error while building the kernel.

Solution: Since Kprobes is of no use if CONFIG_MODULES are disabled, so 
make CONFIG_KPROBES depends on CONFIG_MODULES and we will not have above 
compile problem.